A variable directivity antenna is known, which has its directivity variable to a direction from which a desired radio wave comes. An example of such variable directivity antennas is a dipole antenna with an asymmetrically loaded feed point disclosed in Page 43 of a book “Antenna Engineering Handbook”, First Edition, Eleventh Print, published on Jan. 25, 2001 from The Institute of Electronics, Information and Communication Engineers of Japan.
According to the technique disclosed in this book, a location to be basically fed of a 1.5 wavelength or 2 wavelength multiple-feed point dipole antenna, which is to be fed at a plurality of locations and, therefore, tends to need a relatively complicated feeding system, is loaded with an impedance, and counterelectromotive force is used for controlling current distribution on the dipole antenna. This handbook states that by electrically controlling the load impedance, the dipole antenna can be a variable directivity antenna.
The dipole antenna according to the handbook can receive radio waves only in a single frequency band, but it cannot be used to receive radio waves in a plurality of frequency bands. Furthermore, electrical control of the load impedance is troublesome.
An object of the present invention is to provide a multiple frequency band antenna which has its directivity easily varied at least in one frequency band, and which is capable of receiving radio waves in a plurality of frequency bands.